In 2001, an archaeological survey of the seafloor prior to construction of a natural gas pipeline led to the discovery of U-166 about 45 miles off the Louisiana coast. BP and Shell sponsored additional fieldwork to record detailed images, including a gun on the deck aft of the submarine’s conning tower.

Petroleum companies operating in the Gulf of Mexico’s outer continental shelf are required to provide detailed sonar data in areas that have archaeological potential.

Several federal agencies today review about 1,700 oil and natural gas company surveys every year. The surveys have revealed more than 100 historic shipwrecks. In 2001, scientists at the Minerals Management Service noted that “a German submarine definitely got our attention.”

During World War II, U-boats prowled the Gulf of Mexico to disrupt the vital flow of oil carried by tankers departing ports in Louisiana and Texas.

In just one year, the Kriegsmarine sank 56 Allied ships, including 17 tankers, while losing only one submarine – the Unterseeboot 166.

German submarine predations so threatened the war effort that American government and industry responded with the longest petroleum pipeline project ever undertaken, building the “Big Inch” and “Little Big Inch” from East Texas to Illinois, and as far as New York. See WW II Big Inch and Little Big Inch Pipelines.

But for the U-166, the war was over. Its final resting place remained a mystery for almost 60 years.

The last victim of the U-166 was the passenger freighter Robert E. Lee, sunk by a single torpedo on July 30, 1942, while on its way to New Orleans. Her Naval escort ship, PC-566, rushed in to drop ten depth charges. The U-166 was believed to have escaped. It did not.

Commissioned on March 23, 1942, U-166 today is a war grave in the Gulf of Mexico.

Finding U-166

In 1986, a Shell Offshore vessel using a deep-tow system of the day recorded two close wrecks about 45 miles off the Louisiana coast in 5,000 feet of water.

Thought to be the Robert E. Lee and cargo freighter Alcoa Puritan, it was May 2001 before an autonomous underwater vehicle (AUV) using side scan sonar revealed the U-166. The lost World War II submarine was separated from Robert E. Lee by less than a mile on the sea floor.

The U.S. petroleum industry remains a principle user of advanced underwater technologies for seafloor mapping.

The AUV, which required no cable connection to its mother ship, found the Alcoa Puritan 14 miles away. Learn more about the petroleum industry’s offshore robotics in “Swimming Socket Wrenches.”

The historic submarine’s discovery resulted from the requirement for an archaeological survey of the seafloor prior to construction of a natural gas pipeline by BP and Shell Oil. Six other World War II vessels have been discovered in the course of Gulf of Mexico oil and natural gas surveys.

As a result of the U-166’s discovery, BP and Shell altered their proposed pipeline to preserve the site and government archaeologists notified the U.S. Navy Historical Center of the discovery, notes a 2001 MMS newsletter.

“They, in turn, notified the German Embassy and military attaché,” the MMS article explains. “Since the remains of the U-166’s 52 crewmen are still on board, the German government has declared the site to be a war grave and has requested that it remain undisturbed.”

Gulf of Mexico oil tanker losses led to a petroleum industry achievement: construction of the “Big Inch” and “Little Big Inch” pipelines that connected Texas oilfields to eastern refineries.

Editor’s Note – Since 2011, the Minerals Management Service has become the Bureau of Ocean Energy Management and the Bureau of Safety and Environmental Enforcement.